today, the president is at the white house preparing for his next debate against mitt romney. in a cbs news poll of uncommitted voters taken right after the debate, 50% thought vice president biden won. >> these guys bet against america all the time. >> reporter: or polls gave ryan the edge. >> this is what politicians do when they don't have a record to run on, try to scare people from voting for you. >> reporter: it remains to be seen if last night's showdown will sway voters. historians say the past 8 vice- presidential debates had no effect on the election. danielle nottingham, cbs news, the white house. >>> for more political coverage, just check out our exclusive presidential forum on cbssf.com. every day, the candidates weigh in on a different issue. >>> up next, popping sleeping pills may help you sleep but there are some side effects for those who might have insomnia. >> plus, the final journey begins for endeavour. you're looking live as the space shuttle makes its way through the streets of l.a. we'll tell you where it's headed. >> hi i'm meteorologist lawrence karn